It is known to provide a vehicle with a coasting function which allows the vehicle to reduce driveline losses during a vehicle overrun condition. These strategies are referred to herein as overrun idle coasting, since they are implemented when the driver completely releases the throttle pedal. An overrun idle coasting control system is currently available from Porsche® automobiles. When the accelerator pedal is released, the transmission can be selectively decoupled from the driveline allowing the vehicle to coast without engine braking. While the transmission is decoupled from the driveline, the engine speed can be reduced to an engine idle speed in order to reduce fuel consumption. The appropriate drive gear is engaged to couple the transmission to the driveline when the throttle (accelerator) or brake pedal is depressed. The coasting function can, for example, be utilized on downhill gradients that allow the vehicle to maintain a constant speed.
Under favourable travelling conditions (typically when the vehicle travels on a gently sloping gradient), these overrun idle coasting control systems allow the vehicle to maintain motion without perceptible deceleration. Accordingly, fuel consumption can be reduced. However, coasting control systems in accordance with the prior art may be at conflict with other vehicle systems such as engine-mounted regenerative battery charging systems, which try to capture and utilise energy during the same favourable travelling conditions.
Overrun idle coasting control systems according to the prior art are activated when the driver releases the throttle pedal. However, as the coasting function is not always engaged when the throttle pedal is released, the vehicle deceleration behaviour may vary depending on whether the coasting function is activated. The driver may thus experience unexpected or inconsistent responses from the vehicle, which may negatively affect driver confidence.
U.S. Pat. No. 5,794,170 B discloses a downhill coasting situation detecting device for an automotive vehicle comprising a sensor for detecting an opening degree of a throttle valve; a first derivative calculating device for calculating a first derivative of the vehicle speed; a second derivative calculating device for calculating a second derivative of the vehicle speed and a downhill coasting situation determining device for determining that the automotive vehicle has begun downhill coasting in which the throttle valve opening is zero; the first derivative is positive; and the second derivative is nearly equal to zero. Accordingly, transmission gear down-shifting for obtaining further engine braking can be automatically executed in the downhill coasting situation.
US 2010/0185368 A1 discloses a method and device for controlling a coasting movement of a vehicle such that the vehicle can coast or stop in a smooth manner.
At least in certain embodiments the present invention seeks to overcome or ameliorate at least some of the limitations associated with the prior art arrangements.